With decreasing feature size and more intricate fabrication techniques for wafer-based integrated circuit chips, wafers and the resulting integrated circuit chips have become increasingly sensitive to extraneous or unwanted material on the wafer/chip surface during and after processing. The presence of these unwanted materials either at intermediate fabrication stages or at the end of manufacture often adversely affects product performance reliability. Lack of adequate control of these unwanted materials can result in a loss of yield (reliable chips) and/or the failure of products in use.
Unwanted materials on the wafer/chip surface can be introduced from the external environment (e.g. dust in the air). More often however, unwanted material is introduced as a result of chip fabrication steps which cause deposition of unwanted material on the wafer surface. For example, chemical mechanical polishing (CMP) processes are used to planarize wafers and/or to planarize layers deposited on the wafers (e.g., polycrystalline silicon, tetraethylorthosilicate (TEOS), etc.). Frequently, residual material detached from the wafer in the course of CMP processes remains on the wafer surface as debris. CMP polishing particles may also remain on the wafer surface after the CMP process step. Other unwanted materials may be introduced to the wafer surface during the course of processes such as chemical vapor deposition (CVD), wet etching or dry etching which are frequently used in the manufacture of integrated circuits.
The desire to control the amount of unwanted material on the wafer/chip surface during manufacture has led to the development of a variety of cleaning processes. Most cleaning processes involve the use of liquids which contact the wafer surface. In some instances, the liquid-based cleaning processes may be combined with mechanical cleaning processes (e.g. brushing off the wafer surface) or other cleaning processes. Mechanical energy has also been applied in the form of ultrasonic and/or megasonic energy applied to a cleaning fluid via transducers. The use of megasonic energy has been useful in providing improved cleaning and in lessening the need for concentrated cleaning solutions.
While the use of megasonic energy has provided benefits, there are instances where application of megasonic energy may result in damage to wafers. Also, there is a demand for still further improved cleaning performance, reduced cleaning time and reduced cleaning cost.